When logs are harvested from the forest, the logs are used in many processes. Particular logs may be bound for lumber mills, pulp mills, plywood mills or veneer mills. Many logs are crooked, oversized or have irregularities that make them unsuitable for use in such processes. Bark must be removed before precision chips are produced and before a log can be processed by a veneer lathe. Logs must be uniformly round for the production of usable veneer in a veneer lathe, and can be more efficiently packed in shipping containers or vats for soaking and steaming the logs is the logs are round. Round logs are also required for certain end uses such as posts or poles. In addition, one may desire to process a log into very thin flakes. The very thin wood flakes are used to manufacture chip boards or flake boards.
In the past, the debarking, rounding, sizing and chipping operations have generally been carried out on separate machines. This practice has been inefficient in terms of energy use, time and labor.
Prior debarking apparatus has included ring-type debarkers like that shown in U.S. Pat. No. 3,285,305. In such machines a log passes through a ring fitted with scrapers that rotate around the log rapidly and remove the bark as the log passes through the ring. A disadvantage of the ring-type debarkers is that the diameter of the ring restricts the maximum size log that can be processed. The process is time consuming because the scrapers do not work along the entire length of the log simultaneously. Also, the log handling apparatus provided with ring debarkers often cannot handle logs under a certain length.
Another type of debarker is the slitter disc, as shown in U.S. Pat. No. 2,891,588. Debarking has also been accomplished by rossing and abrading rollers, as shown in U.S. Pat. No. 1,619,151, by tossing a number of logs inside a drum having scrapers or abrading heads mounted on the interior wall of the drum, and by machines which remove the bark by causing a rossing or abrading head to traverse the length of the log back and forth as the log is slowly rotated.
Rounding of crooked logs and reducing their diameter to a size acceptable in further processing steps has been accomplished using a veneer lathe. It has been necessary in the prior art devices to pre-center the log in a lathe charger by engaging the opposite ends of the log with spindles or the like, and placing the log into the veneer lathe to remove radially protruding portions from the log so that it will be round in shape prior to the actual removal of usable veneer sheets. It can be difficult to accurately center or locate the axis of the log when engaging the ends thereof, and therefore excessive amounts of wood may be removed by the lathe in attempting to shape the log before the veneer sheets can be cut. Furthermore, during this process the knife of the veneer lathe engages the entire length of the log, and therefore requires large amounts of energy to remove waste material from the log.
Many prior art devices have been developed for reducing logs to chips. A widely used device propels the log end-on at angle into a rotating disk upon the face of which are mounted cutter knives. Examples of such devices as shown in U.S. Pat. Nos. 3,732,907 and 3,746,062. Logs have also been propelled against cutter knives protruding from the exterior of rotary drums, both end-on, as shown in U.S. Pat. Nos. 3,285,305; 3,304,970; and 3,394,744, or along the length of a log, as shown in U.S. Pat. No. 2,951,518. Yet another type of chipping apparatus provides a rotating head which chips away the side of the log as the log moves longitudinally past the head, as shown in U.S. Pat. Nos. 2,889,859 and 3,240,245. A disadvantage common to all such prior chippers is that the cutter knives traverse long paths through the logs. Thus, the devices have large horsepower requirements to provide the cutter knives with sufficient surge and force to carry them through the log. In most prior chippers, the cutter knives must, at some point in the consumption of the log, traverse the full diameter of the log. A further typical disadvantage of prior art debarkers, chippers, flakers and rounding apparatus is a necessity for complex and expensive log handling equipment required to guide the logs into engagement with the operative cutting or abrading elements, and to remove the processed log or chips therefrom. The nature of the handling apparatus or the operative cutting abrading elements often limits the maximum diameter of the logs that can be processed. Cutter knives which must make long cuts each time they engage the wood have relatively short lives and must be repeatedly replaced. Thus, there has been a need in the art for an apparatus capable of efficiently debarking, rounding, sizing and chipping logs harvested from the forest.
One prior device that attempts to alleviate some of the problems described above is disclosed in U.S. Pat. No. 4,444,234. This device is capable of debarking, rounding and chipping the log in one operation. The device has a large rotating cylinder with a plurality of knives on the periphery of the cylinder. The log is introduced into the apparatus and horizontally engages the cylinder. Although the apparatus described in the U.S. Pat. No. 4,444,234 will debark, round, and chip a log in one operation, the replacement of a knife in the cylinder is cumbersome and difficult. Another problem is that the cylinder must be of a certain diameter to provide sufficient structure between the adjacent knives. If the drum material between knives is insufficient, the drum could warp during operation.
Conventional wood flakers use the surface of the knife holder to gauge the depth of the cut. This causes a stability problem since the log tends to bounce against the surface of the knife holder. The resulting vibration causes the knife edge to dull more quickly, and may cause the wood flakes to vary in thickness. Wood flakes that vary in thickness can be unacceptable for many industrial purposes.